The nature of acquired resistance to infection with Treponema pallidum has not been elucidated. We have shown that infection with T. pallidum induced a nonspecific resistance to a subsequent challenge with Listeria monocytogenes and that this nonspecific resistance to listeria can be transferred to normal rabbits using thymus-derived lymphocytes (T cells). This provides evidence that T. pallidum induces cell-mediated immunity (CMI). Although the detection of nonspecific resistance to Listeria in syphilitic rabbits is of interest, no evidence has been reported concerning the participation of CMI in establishing specific resistance to infection with T. pallidum. The objectives of this proposal are to determine: 1) the involvement of T cells and bursa-equivalent lymphocytes (B cells) in an infection with T. pallidum, and 2) if specific resistance to infection with T. pallidum can be transferred to normal recipients using syngeneic lymphocytes obtained from syphilitic immune rabbits. The temporal relationships between development and regression of syphilitic lesions and the infiltration of T and B cells into these lesions will be studied, as well as the in vivo distribution and quantity of T cells, B cells, and T. pallidum in the cutaneous lesions, lymph nodes and spleens of syphilitic rabbits. The responsiveness of lymphoid cells from syphilitic rabbits will be studied in vitro stimulation of T and B cells by specific mitogens and specific treponemal antigens. In addition, attempts to adoptively immunize rabbits to syphilitic infection and to alter the course of infection with T. pallidum in thymectomized and neonatal rabbits will be made with defined lymphoid and/or macrophage populations.